Assemblies including shape memory alloy fittings and composite structural members

ABSTRACT

Provided are assemblies having composite structures interlocked with shape memory alloy structures and methods of fabricating such assemblies. Interlocking may involve inserting an interlocking protrusion of a shape memory alloy structure into an interlocking opening of a composite structure and heating at least this protrusion of the shape memory alloy structure to activate the alloy and change the shape of the protrusion. This shape change engages the protrusion in the opening such that the protrusion cannot be removed from the opening. The shape memory alloy structure may be specifically trained prior to forming an assembly using a combination of thermal cycling and deformation to achieve specific pre-activation and post-activation shapes. The pre-activation shape allows inserting the interlocking protrusion into the opening, while the post-activation shape engages the interlocking protrusion within the opening. As such, activation of the shape memory alloy interlocks the two structures.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/323,529, entitled: “Assemblies Including Shape Memory Alloy Fittingsand Composite Structural Members” filed on Jul. 3, 2014, which isincorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

This disclosure generally relates to assemblies including shape memoryalloy fittings and composite structural members. More specifically, thisdisclosure relates to assemblies in which shape memory alloy fittingsinterlock with composite structural members when the shape memory alloysof the fittings are activated by heating and the fittings change theirshape.

BACKGROUND

Composite materials are becoming increasing popular for variousapplications, such as aircraft. A composite is a material that is formedfrom two or more different components. Characteristics of the compositemay be quite different than that of its individual components. Theindividual components may remain separate and distinct in a structureformed from the composite. Once a composite structure is formed, thestructure generally should not be disturbed to maintain integrity of thecomponents forming this structure. This limitation makes it difficult toform structural and other types of connections to composite structures.

SUMMARY

Provided are assemblies having composite structures interlocked withshape memory alloy structures and methods of fabricating suchassemblies. Interlocking may involve inserting an interlockingprotrusion of a shape memory alloy structure into an interlockingopening of a composite structure and heating at least this protrusion ofthe shape memory alloy structure to activate the alloy and change theshape of the protrusion. This shape change engages the protrusion in theopening such that the protrusion cannot be removed from the opening. Theshape memory alloy structure may be specifically trained prior toforming an assembly using a combination of thermal cycling anddeformation to achieve specific pre-activation and post-activationshapes. The pre-activation shape allows inserting the interlockingprotrusion into the opening, while the post-activation shape engages theinterlocking protrusion and opening. As such, activation of the shapememory alloy interlocks the two structures.

In some embodiments, an assembly comprises a first structure and asecond structure. The first structure comprises a composite material andmay be referred to as a composite structure or a composite structuralmember. In some embodiments, the composite material maybe any textilecomposite. The second structure comprises a shape memory alloy and maybe referred to as a shape memory alloy structure or a shape memory alloyfitting or simply a fitting. The first structure interlocks with thesecond structure such that an interlocking protrusion of the secondstructure extends into an interlocking opening of the first structure.The interlocking protrusion is engaged within the interlocking openingwhen the first structure is interlocked with the second structure. Whenengaged, the interlocking protrusion is not movable with respect to theinterlocking opening. Furthermore, the interlocking protrusion isconfigured to change it shape when the interlocking protrusion is heatedabove the activation temperature of the shape memory alloy used to makethe second structure. The activation temperature is sometimes referredto as a transformation temperature as it corresponds to phasetransformation of the shape memory alloy as further described below. Theshape change engages the interlocking protrusion with the interlockingopening. Specifically, this engagement prevents the interlockingprotrusion from moving with respect to the interlocking opening, and thesecond structure remains attached to the first structure.

In some embodiments, the shape memory alloy is a one-way shape memoryalloy. This type of alloy changes the shape of the interlockingprotrusion of the second structure during heating but not during thesubsequent cooling. More specifically, the interlocking protrusionchanges its shape when the interlocking protrusion is heated above theactivation temperature. However, the interlocking protrusion does notchange its shape again when the interlocking protrusion is subsequentlycooled below the activation temperature. In some embodiments, theactivation temperature is at least about 350° F. or, more specifically,at least about 400° F. depending on the materials used.

In some embodiments, the assembly also comprises a third structure. Thethird structure may be also made from the same shape memory alloy thatforms the second structure. Alternatively, the third structure may bemade from a different shape memory alloy. The first structure interlockswith the third structure such that an interlocking protrusion of thethird structure extends into an additional interlocking opening of thefirst structure. The interlocking protrusion is engaged with theadditional interlocking opening when the first structure is interlockedwith the third structure. When engaged, the interlocking protrusion isnot movable with respect to the additional interlocking opening. Theinterlocking protrusion is configured to change its shape when theinterlocking protrusion is heated above the activation temperature ofthe shape memory alloy, which may be at least about 350° F. or even atleast about 400° F., in some embodiments. Furthermore, the interlockingprotrusion is configured to engage with the additional interlockingopening of the first structure thereby preventing the interlockingprotrusion of the third structure from moving with respect to theadditional interlocking opening of the first structure. In someembodiments, the second structure and the third structure areinterlocked with each other in addition to being individuallyinterlocked with the second structure. Furthermore, the second structureand the third structure may form an enclosing sleeve around the firststructure.

In some embodiments, the assembly also comprises an adhesive. Theadhesive may be disposed between the first structure and the secondstructure. The adhesive may bond the first structure to the secondstructure in addition to interlocking the first structure and the secondstructure.

In some embodiments, the interlocking protrusion of the second structurecomprises a first outer protrusion corner and a second outer protrusioncorner. The distance between the first outer protrusion corner and thesecond outer protrusion corner may be configured to increase the whenthe interlocking protrusion is heated above the activation temperatureof the shape memory alloy, which may be at least about 350° F. or evenat least about 400° F. in some embodiments. This increase in thedistance may be used for interlocking the first and second structures.

In some embodiments, the interlocking opening of the first structurecomprises a first outer opening corner and a second outer openingcorner. The distance between the first outer opening corner and thesecond outer opening corner is less than the distance between the firstouter protrusion corner and the second outer protrusion corner of thesecond structure when the first structure interlocked with the secondstructure. Prior to interlocking, the distance between the first outeropening corner and the second outer opening corner is greater than thedistance between the first outer protrusion corner and the second outerprotrusion corner.

Provided also is a method of forming an assembly. The method maycomprise inserting an interlocking protrusion of a second structure intoan interlocking opening of a first structure. The first structurecomprises a composite material. The second structure comprises a shapememory alloy. After inserting the interlocking protrusion into theinterlocking opening, the method proceeds with heating at least theinterlocking protrusion of the second structure. In some embodiments,other portions of the second structure may be heated as well. Duringheating, the interlocking protrusion of the second structure changesshape and engages the interlocking opening of the first structure suchthat the interlocking protrusion of the second structure is not movablerelative to the interlocking opening of the first structure when thefirst structure is interlocked with the second structure.

In some embodiments, the method also comprises training the secondstructure. The training may comprise heating the interlocking protrusionof the second structure. While heated, the shape of the interlockingprotrusion of the second structure may be changed. In some embodiments,the training comprises cooling the interlocking protrusion of the secondstructure and, while cooled, changing the shape of the interlockingprotrusion of the second structure.

In some embodiments, the interlocking protrusion of the second structurecomprises a first outer protrusion corner and a second outer protrusioncorner. The interlocking opening of the first structure comprises afirst outer opening corner and a second outer opening corner. Prior toheating, the distance between the first outer protrusion corner and thesecond outer protrusion corner of the interlocking protrusion of thesecond structure is less than the distance between the first outeropening corner and the second outer opening corner of the interlockingopening of the first structure. However, after heating, the distancebetween the first outer protrusion corner and the second outerprotrusion corner of the interlocking protrusion of the second structureis greater than the distance between the first outer opening corner andthe second outer opening corner of the interlocking opening of the firststructure.

In some embodiments, the method also comprises consolidating thecomposite material of the first structure prior to inserting theinterlocking protrusion of the second structure into the interlockingopening of the first structure. The method may also comprise, afterconsolidating the composite material of the first structure, forming theinterlocking opening in the first structure. The method may comprise,prior to heating at least the interlocking protrusion of the secondstructure, inserting an interlocking protrusion of a third structureinto an additional interlocking opening of the second structure. In someembodiments, the interlocking protrusion of the third structure isinserted into the additional interlocking opening of the secondstructure. In some embodiments, prior to heating at least theinterlocking protrusion of the second structure, cooling of at least theinterlocking protrusion of the second structure is performed. In someembodiments, the method further comprises disengaging the secondstructure from the first structure. This operation may be performedafter the assembly is removed from the operational environments, e.g.,an aircraft placed into repair or maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described examples of the disclosure in general terms,reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein like reference charactersdesignate the same or similar parts throughout the several views, andwherein:

FIGS. 1A and 1B are schematic perspective and sectional views of anassembly including a composite structure interlocked with two shapememory alloy structures, according to one aspect of the presentdisclosure;

FIG. 2A is a sectional view of the composite structure, which is a partof the assembly shown in FIGS. 1A and 1B, according to one aspect of thepresent disclosure;

FIG. 2B is a sectional view of the shape memory alloy structure, whichis a part of the assembly shown in FIGS. 1A and 1B, according to oneaspect of the present disclosure;

FIG. 3 is a process flowchart corresponding to a method of forming anassembly including a composite structure interlocked with at least oneshape memory alloy structure, according to one aspect of the presentdisclosure;

FIGS. 4A-4C are sectional views of the composite structure and shapememory alloy structure during various stages of forming an assemblyincluding these two structures, according to one aspect of the presentdisclosure;

FIG. 5 is a block diagram of an aircraft production and servicemethodology that may utilize one or more assemblies, each including acomposite structure interlocked with at least one shape memory alloystructure;

FIG. 6 is a schematic illustration of an aircraft that may utilize oneor more assemblies, each including a composite structure interlockedwith at least one shape memory alloy structure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented concepts. Thepresented concepts may be practiced without some or all of thesespecific details. In other instances, well known process operations havenot been described in detail so as to not unnecessarily obscure thedescribed concepts. While some concepts will be described in conjunctionwith the specific examples, it will be understood that these examplesare not intended to be limiting.

Reference herein to “one example” or “one aspect” means that one or morefeature, structure, or characteristic described in connection with theexample or aspect is included in at least one implementation. The phrase“one example” or “one aspect” in various places in the specification mayor may not be referring to the same example or aspect.

Introduction

Composite materials are being rapidly adopted for various newapplications because of their light weight and exceptional structuralcapabilities. For example, some solid and hollow composite structureshave demonstrated high energy absorption characteristics making thesestructures particular suitable for applications, such as load bearingstructure in aircraft and other similar applications. Textile-basedmaterials are examples of composite materials that are considered forvarious applications requiring high impact, crash, and fatigueresistance. The textile composites, such as near-net shaped components,are often fabricated using braiding techniques. Many unique propertiesof the textile composites come from the yarn continuity and mechanicalinterlacing of the yarn within structures formed from these composites.These features prevent crack propagation at the yarn intersection and,as a result, increase the fatigue life. At the same time, the fibercontinuity does not limit the application of these composites to axialand bending loads, such as load bearing beams and shafts.

Complex structural geometries and different types of loads often requireconnecting multiple structures in order to establish load transfermechanisms. As such, one or more joints along the length of the textilecomposites are often necessary. Fabrication of each joint delays themanufacturing process and can negatively impact the strength of theprimary structure.

Provided are assemblies including composite structures interlocked withshape memory alloy structures. Specifically, each composite structuremay be interlocked with one or more shape memory alloy structures. Alsoprovided are methods of forming such assemblies. Some shape memoryalloys exhibit unique properties, which are not found in other materialsand which are particularly helpful to forming structural connectionswith composite structures in various assemblies. The properties ofparticular importance herein are pseudo-elasticity and shape memoryeffect. Pseudo-elasticity, which is sometimes also referred to assuper-elasticity, is an elastic response to an applied stress.Pseudo-elasticity is caused by a phase transformation between theaustenitic and martensitic phases of the shape memory alloys. Apseudo-elastic material returns to its previous shape after the removalof even relatively high applied strains. Some examples of suitable shapememory alloys include nickel-titanium alloy, copper-zinc-aluminumalloys, copper-aluminum-nickel alloys and other alloys. Nickel-titaniumalloys may be particularly suitable for connecting to compositestructures because of the smooth and controlled force exerted uponactivation of these alloys, which prevents stress concentration on thesurface of the composite structures.

The shape memory alloys display two distinct crystal structures orphases, i.e., a martensite phase and austenite phase. Temperature andinternal stresses, which play a part in super-elasticity, determine thecurrent phase of a shape memory alloy. Specifically, the martensitephase exists at lower temperatures, while the austenite phase exists athigher temperatures. The temperature dividing these two phases may bereferred to as an activation temperature. When a shape memory alloy isin the martensite phase, the alloys can be easily deformed into anyshape. When this shape memory alloy is later heated above its activationtemperature, it goes through transformation from the martensite phaseinto the austenite phase. In the austenite phase, the shape memory alloyreturns to its original shape, which is the shape it had before it wasdeformed. The shape memory alloys may be trained to set theirdeformation path and joint strength for particular applications, such asinterlocking with composite structures without creating stressconcentration points often associated with other types of connections,such as fasteners.

A shape memory alloy structure may have a shrink-fit configuration that,when activated, fits around the surface of a composite structure towhich the shape memory alloy structure is connected or, morespecifically, interlocked. The post-recovery interference of the shapememory alloy structure in this assembly, which may be also referred toas a contact strain, may be between about 0.5% and 3% or, morespecifically, between about 1% and 2%, such as about 1.5% based on thepre-activation size of the shape memory alloy structure. Post-recoveryinterference values below these ranges (e.g., below 1% or, morespecifically, below 0.5%) may not provide sufficient interlocking, andthe shape memory alloy structure may disengage from the compositestructure during operation of the assembly. On the other hand, largerpost-recovery interference values (e.g., greater than 2%, or morespecifically, greater than 3%) may cause excessive stresses within theassemblies and may compromise the integrity of the composite structures.

Furthermore, shape memory alloy structures may be designed accountingfor tolerances of the shape memory alloy structures as well astolerances of composite structures that the shape memory alloystructures are designed to interlock. The shape memory alloy structuresmay be also designed to account for various installation clearances.Finally, assemblies including shape memory alloy structures interlockedwith composite structures provide sufficient radial flexibility andadequate interfacial bonding strength.

In some embodiments, an assembly may include one or more interlockingmechanisms that engage a composite structure with one or more shapememory alloy structures that form the same assembly. Specifically, anassembly may have three such interlocking mechanisms formed by two shapememory alloy structures and one composite structure. Each shape memoryalloy structure may form a separate interlocking mechanism with thecomposite structure. For example, each shape memory alloy structure mayinclude an interlocking protrusion extending into a correspondinginterlocking opening of the composite structure. The interlockingprotrusion is engaged and not movable relative the interlocking openingwhen the composite structure is interlocked with the shape memory alloystructure. The two shape memory alloy structures may be connected duringinstallation and this connection may form a third interlockingmechanism. Each interlocking mechanism may provide some resistance toaxial or bending displacements and may be used to transfer some of theloads in these directions.

When multiple interlocking mechanisms are used in the same assembly,each mechanism provides a separate path between the composite structureand one or more shape memory alloy structures. These paths may be viewedas redundant paths. These paths allow the composite structure tocontinue performing even if the interfacial bond, which may beestablished by an adhesive, between the composite structure and shapememory alloy structure fails. This redundancy may be used for variouscritical structural applications, such as aircraft applications.

The shape memory alloy structure may also be used as a loading mechanismwithout altering the outer and/or inner diameters of a linear compositestructure (e.g., hollow tubes) or the inner spatial volume of anycomposite structured having variable shapes to which this shape memoryalloy structure is connected. This feature preserves structuralcharacteristics of the composite structures because, for example, thebraiding patterns are retained in textile-type composite structures.Retaining the braiding patterns preserves high processing speeds andmaintains structural integrity of the composite structures even thoughexternal connections are formed by interlocking shape memory alloystructure to the external surfaces of the composite structures. Theproposed assemblies allow forming multiple branching joints on the samecontinuous composite structure without creating any weakened portions inthis composite structure. Furthermore, these assemblies may be formedusing non-uniform composite structures, such as structures with variablecross-sections or tapered structures.

The process of forming such assemblies may involve training shape memoryalloy structures in order for these structures to keep one shape duringinstallation, which may be referred to as a pre-activation shape, andanother shape after installation, which may be referred to as apost-activation shape. Specifically, the pre-activation shape allowsinserting an interlocking protrusion of the shape memory allow structureinto an interlocking opening of the composite structure. In thepre-activation shape, the distance between the outer protrusion cornersof the interlocking protrusion of the second structure is less than thedistance between the outer opening corners of the interlocking openingthereby allowing the interlocking protrusion to be inserted into theinterlocking opening. The post-activation shape engages the interlockingprotrusion and interlocking opening. In the post-activation shape, thedistance between the outer protrusion corners of the interlockingprotrusion of the second structure is greater than the distance betweenthe outer opening corners of the interlocking opening. This change inshape allows interlocking the shape memory alloy structure with thecomposite structure.

Due to geometric complexities, the change in shape may be localized tothe interlocking protrusion or one or more portions thereof.Specifically, the interlocking protrusion may be cooled prior toinserting it into the interlocking opening and then allowed to heat up,e.g., to the room temperature or some other temperature. Variouslocalized cooling techniques, such as partial immersion into a coolingliquid (e.g., liquid nitrogen), thermo-electric cooling, refrigerationcooling, etc. may be used. Once the shape memory alloy structure is inplace, the temperature of the cooled portion may increase due to theheat transfer from the environment and/or from the heating source. Theheating may cause expansion of the portion of the shape memory alloystructure protruding into the composite structure thereby forming aninterlocking mechanism.

Assembly Examples

FIG. 1A is a perspective schematic view of assembly 100 including firststructure 102 comprising a composite material and a second structure 104comprising a shape memory alloy, in accordance with some embodiments.First structure 102 may be also referred to as a composite structure,while second structure 104 may be referred to as a shape memory alloystructure or a fitting. FIG. 1A also illustrates optional thirdstructure 106. One having ordinary skill in the art would understandthat assembly 100 may include any number of shape memory alloystructures, such as one shape memory alloy structure, two shape memoryalloy structures, three shape memory alloy structures, and so on. Whenmultiple shape memory alloy structures are used in the same assembly,these structures may interlock with each other in addition to beingindividually interlocked with a composite structure. Furthermore,multiple shape memory alloy structures may form an enclosing sleevearound the composite structure.

As shown in FIG. 1B and further described below with reference to FIGS.3 and 4A-4C, first structure 102 interlocks with second structure 104such that interlocking protrusion 210 of second structure 104 extendsinto an interlocking opening 200 of first structure 102. Interlockingprotrusion 210 is engaged with interlocking opening 200 when firststructure 102 is interlocked with second structure 104. In this engagedstate, interlocking protrusion 210 is not able to move with respect tointerlocking opening 200. Interlocking protrusion 210 is configured tochange its shape when interlocking protrusion 210 is heated above theactivation temperature of the shape memory alloy, which may be at leastabout 350° F. or even at least about 400° F. in some embodiments. Whenthe shape is changed during installation, interlocking protrusion 210engages interlocking opening 200 as shown in FIG. 1B.

First structure 102 comprises a composite material. The compositematerials may include polyaryls, such as polyetheretherketone (PEEK),polyetherketoneketone (PEKK), and polyphenylenesulphide (PPS), as wellas other thermoplastics. In some embodiments, the composite material ofthe first structure is braided. Braided composite materials include afabric constructed by the intertwining of two or more yarn systems toform an integral structure. Braided composites have superior toughnessand fatigue strength in comparison, for example, to filament woundcomposites. Specifically, woven fabrics have orthogonal interlacement,while the braids can be constructed over a wide range of angles. Braidscan be produced either as seamless tubes or flat fabrics with acontinuous selvedge. Braided composites exhibit superior strength andcrack resistance in comparison to, for example, broadcloth compositesdue to fiber continuity in the braided composites.

Second structure 104 comprises a shape memory alloy. Suitable shapememory alloys include, but are not intended to be limited to, nickeltitanium based alloys, indium-titanium based alloys, nickel aluminumbased alloys, copper based alloys (e.g., copper-zinc alloys,copper-aluminum alloys, copper-gold, and copper-tin alloys), goldcadmium based alloys, iron-platinum based alloys, iron palladium basedalloys, silver-cadmium based alloys, indium-cadmium based alloys,manganese-copper based alloys, and the like. The alloys can be binary,ternary, or any higher order so long as the alloy composition exhibits ashape memory effect, e.g., change in shape orientation, changes inflexural modulus properties, damping capacity, and the like. Oneparticular example of a shape memory alloy is a nickel-titanium basedalloy, commercially available under the name of NITINOL (Nickel TitaniumNaval Ordnance Laboratory). In some embodiments, the shape memory alloyused for second structure 104 is a one-way shape memory alloy. In thiscase, interlocking protrusion 210 of second structure 104 changes shapewhen it is heated above the activation temperature of the alloy but doesnot change the shape when interlocking protrusion 210 is subsequentlycooled below the activation temperature. It should be noted that manyshape memory alloys used for other applications, such as medicalimplants, are two-way shape memory alloys. The two-way shape memoryalloys exhibit reversible shape change of materials with thermalcycling, in other words, the shape changes during both heating andcooling. In some embodiments, the same material can be used as eitherone-way shape memory alloy or a two-way shape memory alloy. Thischaracteristic may depend on the training of the structure. Of course,the composition will also affect this characteristic.

In some embodiments, the activation temperature of the shape memoryalloy used for second structure 104 is based on the alloy composition.For example, the activation temperature range of Ni—Ti alloy may bebetween about −50° F. and 500° F. The shape memory alloy may bespecifically configured for other activation temperatures as well. Forexample, the activation temperature may be at least about 350° F. oreven at least about 400° F., in some embodiments. In some embodiments,the activation temperature exceeds the maximum operating temperature by,for example, at least about 50° F. or even at least about 100° F. Adifferent activation temperature may be used for another shape memoryalloys structure, if this other structure interlocks with the samecomposite structure. The difference in activation temperatures may be atleast about 50° F. or even at least about 100° F.

As shown in FIGS. 1A and 1B, assembly 100 may also include thirdstructure 106. Third structure 106 may also comprise a shape memoryalloy. In some embodiments, third structure 106 and second structure 104may be made from the same material. Third structure 106 (and any otheradditional shape memory alloy structure that may be used in the sameassembly) may interlock with first structure 102 in a manner similar towhich second structure 104 interlocks with first structure 102.Specifically, first structure 102 may interlock with third structure 106such that an interlocking protrusion of third structure 106 extends intoan additional interlocking opening of first structure 102. Theinterlocking protrusion is engaged to the additional interlockingopening when first structure 102 is interlocked with third structure106. The engagement prevents the interlocking protrusion from movingwith respect to the additional interlocking opening. The interlockingprotrusion is configured to change its shape when this protrusion isheated above the activation temperature of the shape memory alloy andengage with the additional interlocking opening.

Furthermore, second structure 104 and third structure 106 may interlockwith each other as, for example, shown in FIG. 1B. Second structure 104may include interlocking step 116 that snugly fits into a correspondinginterlocking groove of third structure 106. Likewise, third structure106 may include interlocking step 114 that snugly fits into acorresponding interlocking groove of second structure 104. Thesecombinations of interlocking steps and grooves engage the bottom end ofsecond structure 104 and the bottom end of third structure 106 in the Xdirection as shown in FIG. 1B. The interlocking steps and grooves may beconfigured such that the bottom end of second structure 104 can moverelative to the bottom end of third structure 106 in the Z direction,for example during installation of second structure 104 and thirdstructure 106 on first structure 102 and, more specifically, whileinterlocking second structure 104 with third structure 106. In someembodiments, second structure 104 and third structure 106 may be furtherinterlocked such that the bottom ends of these structures cannot movewith respect to each other in the Z direction.

In some embodiments, second structure 104 and third structure 106 forman enclosing sleeve around first structure 102 as, for example, shown inFIG. 1B. As described above, bottom ends of second structure 104 andthird structure 106 may interlock. The top ends of second structure 104and third structure 106 may directly interface and compress against eachother. As further described below, the top ends of second structure 104and third structure 106 may be configured as flanges for attaching toeach other and, in some embodiments, to other external structures. FIG.1A illustrates second structure 104 and third structure 106 havingopenings in these flanges that are aligned coaxially during installationof second structure 104 and third structure 106 on first structure 102.

In some embodiments, assembly 100 may also include an adhesive disposedbetween first structure 102 and second structure 104. The adhesive maybond these two structures and prevent separation of these structures inaddition to various interlocking features described elsewhere.

FIG. 2A is a schematic cross-sectional view of first structure 102, inaccordance with some embodiments. While first structure 102 is shown tohave a substantially round cross-section shape, first structure 102 mayhave any shape, such as square, rectangular, irregular, etc. It shouldbe noted that at least a portion of the external surface shape of firststructure 102 may correspond to the internal surface shape of secondstructure 104 to ensure adequate surface contact between the twostructures. Furthermore, first structure 102 is shown to be hollow,solid composite structures are also within the scope of this disclosure.

First structure 102 includes interlocking opening 200 for interlockingwith second structure 104 or some other structure. In some embodiments,first structure 102 includes multiple interlocking openings, such asinterlocking opening 200 and interlocking opening 203 as shown in FIG.2A. Each interlocking opening may be configured to interlock with adifferent shape memory alloy structure. For example, interlockingopening 200 may be configured to interlock with second structure 104(shown in FIGS. 1A and 1B), while interlocking opening 203 may beconfigured to interlock with third structure 106 (shown in FIGS. 1A and1B). In some embodiments, two or more interlocking openings may be usedto interlock with the same shape memory alloy structure. Multipleinterlocking openings may have the same configuration or differentconfigurations in order to selectively interlock only with particularother structures. While this disclosure focuses on examples in which acomposite structure has one or more interlocking openings and in which ashape memory alloy structure has a corresponding interlockingprotrusion, other examples, in which a composite structure has one ormore interlocking protrusions and in which a shape memory alloystructure has a corresponding interlocking opening, are also within thescope.

Interlocking opening 200 may include first outer opening corner 202 aand second outer opening corner 202 b. Interlocking opening 200 may alsoinclude first inner opening corner 204 a and second inner opening corner204 b. These four corners define the boundary of interlocking opening200. The distance between first outer opening corner 202 a and secondouter opening corner 202 b may be less than the distance between firstinner opening corner 204 a and second inner opening corner 204 b. Thisdifference in the distances defines the tapered profile of interlockingopening 200 and provides interlocking functionality. Specifically, whena pre-shrunk interlocking protrusion is inserted into interlockingopening 200, the outer protrusion corners of this pre-shrunkinterlocking protrusion may be able to pass between first outer openingcorner 202 a and second outer opening corner 202 b. Later, theinterlocking protrusion is expanded due to the shape memory alloy effect(and, e.g., heating) and its outer protrusion corners may extend tofirst inner opening corner 204 a and second inner opening corner 204 b.In this expanded form, the interlocking protrusion does not engageinterlocking opening 200 and pass through the first outer opening corner202 a and second outer opening corner 202 b because the distance betweenfirst outer opening corner 202 a and second outer opening corner 202 bis now less than the distance between the outer protrusion corners ofthe expanded interlocking protrusion. The installation and interlockingoperations are further described below with reference to FIGS. 3 and4A-4C.

The features of interlocking opening 200 may prevent another structure,which is interlocked with first structure 102, from moving relative tofirst structure 102 in the X direction as shown in FIG. 2A. Furthermore,interlocking opening 200 as well as other interlocking openings mayprevent other structures extending into these openings from rotationaround the Y axis. Overall, interlocking and other types of engagementbetween first structure 102 and one or more other structures may providelinear and rotational support along each of the three axes.

FIG. 2B is a schematic cross-sectional view of second structure 104, inaccordance with some embodiments. As noted above, second structure 104is made from a shape memory alloy. The shape memory alloy may be trainedto change its shape depending on the temperature of second structure104. It should be noted that different portions of second structure 104may respond differently to temperature changes. In some embodiments,outer protrusion corners 212 a and 212 b can be locally trained.

Second structure 104 includes interlocking protrusion 210, which may beinserted, e.g., into interlocking opening 200 of first structure 102.Interlocking protrusion 210 may include first outer protrusion corner212 a and second outer protrusion corner 212 b. Interlocking protrusion210 may also include first inner protrusion corner 214 a and secondinner protrusion corner 214 b. These four corners define the boundary ofinterlocking protrusion 210, which in its activated state may betapered. Furthermore, this activate state boundary of interlockingprotrusion 210 may correspond to the boundary of an interlocking openingwith which this interlocking protrusion 210 engages. The distancebetween first outer protrusion corner 212 a and second outer protrusioncorner 212 b of interlocking protrusion 210 may change duringinstallation of second structure 104. For example, prior toinstallation, the distance between first outer protrusion corner 212 aand second outer protrusion corner 212 b may be less than the distancebetween first inner protrusion corner 214 a and second inner protrusioncorner 214 b. Later (i.e., during activation of the shape memory alloy),the shape of interlocking protrusion 210 may change such that thedistance between first outer protrusion corner 212 a and second outerprotrusion corner 212 b becomes greater than the distance between firstinner protrusion corner 214 a and second inner protrusion corner 214 b.Specifically, the distance between first outer protrusion corner 212 aand second outer protrusion corner 212 b is configured to increase wheninterlocking protrusion 210 of second structure 104 is heated above theactivation temperature of the shape memory alloy, which may be at leastabout 350° F. or even at least about 400° F. This increase in distancemay be used for interlocking as described below with reference to FIGS.3 and 4A-4C.

Second structure 104 may include other protrusions, such as protrusions216 a-216 c shown in FIG. 2B. These protrusions may be used to engagefirst structure 102 and other structures, such as third structure 106 asshown in FIG. 1B. Second structure 104 may also include flange 220 formaking mechanical connections to second structure. For example, flange220 may include opening 222 allowing mechanical fasteners to protrudethrough flange 220.

Processing Examples

FIG. 3 is a process flowchart corresponding to a method 300 of formingan assembly of a composite structure and a shape memory alloy structure,in accordance with some embodiments. Various examples of assemblies andits components are described above with reference to FIGS. 1A-1B and2A-2B. In some examples, an assembly may include multiple shape memoryalloy structures, such as two shape memory alloy structures, interlockedwith the same composite structure. One or more shape memory alloystructure may form a sleeve around a composite structure. After formingan assembly, the shape memory alloy structure may be connected to one ormore external structures and be used for load transfer between theseexternal structures and the composite structure of the assembly. Asnoted above, in some applications, shape memory alloy structures may bereferred to as fittings.

Method 300 may commence with training one or more shape memory alloystructures, such as a second structure comprising a shape memory alloyand, in some examples, an optional third structure comprising the sameshape memory alloy or a different shape memory alloy, as shown inoperation 302. Training operation 302 may involve heating at least aportion of the second structure that is designed to overlap with aportion of a composite structure, i.e., the first structure in thisexample. This heated portion of the second structure may be aprotrusion. In some embodiments, training operation 302 involves heatingthe interlocking protrusion and, while heated, changing the shape of theinterlocking protrusion. Training operation 302 may also involve coolinginterlocking protrusion of the second structure and, while cooled,changing the shape of the interlocking protrusion. A brief descriptionof the training operation will now be provided. A shape memory alloy hastwo phases, each with a different crystal structure and thereforedifferent properties. One phase is a high temperature phase, which isreferred to as an austenite (A) phase. The other phase is a lowtemperature phase, which is referred to as a martensite (M) phase. Theunique property of the shape memory alloy is the result of a martensiticphase transformation that occurs between the high temperature phase (theaustenite phase) and the different variants of the low temperature phase(the martensite phase). Under stress-free cooling below thetransformation temperature, the austenite phase is converted into atwinned martensite phase. When the twinned martensite phase is subjectedto an applied stress that is large enough but lower than the permanentplastic yield stress of the martensite phase, the martensite phase maydetwin by reorienting a certain number of variants. The detwinningprocess results in a macroscopic shape change. The material is thenelastically unloaded, and the detwinned martensitic state is retained.Upon heating in the absence of stress, the reverse transformationinitiates as the temperature increases where only the parent austeniticphase exists. Since there is no permanent plastic strain generatedduring detwinning, the original shape of the shape memory alloy isregained.

The range of activation temperatures that correspond to macro-structuralchanges in depend on the composition. For example, Ni—Ti alloys haveactivation temperatures of between about −50° F. and +500° F. Inaddition, this range can be controlled or adjusted if the shape memoryalloy is subjected to low or high temperature thermo-mechanicaltreatment and/or post-deformation annealing.

It should be noted that the composite structure, i.e., the firststructure in this example, may have a set shape prior to itsinterlocking with the shape memory alloy structure during operations312-316. To form this set shape, method 300 may involve consolidatingthe first structure during operation 304 and/or forming an opening(e.g., an interlocking opening) in the first structure during operation306. Consolidation operation 304 may involve subjecting the firstoperation to a high temperature and/or high pressure to increase densityand reduce the volume occupied by voids. In some embodiments, the voidcontent after the consolidation operation is less than 5% by volume oreven less than 1% by volume. This set shape may be used to design andtrain one or more shape memory alloy structures that are laterinterlocked with the first structure.

In some embodiments, prior to inserting an interlocking protrusion ofthe second structure into an interlocking opening of the firststructure, method 300 involves cooling the interlocking protrusionduring operation 310. The cooling process may change the shape of theinterlocking protrusion and allow it to be inserted into theinterlocking opening. Specifically, the cooling may reduce the distancebetween the two outer protrusion corners of the interlocking protrusion.Localized cooling may be used such that most of the second structureremains at its initial temperature during and after operation 310.Specifically, the interlocking protrusion of the second structure may becooled to room temperatures.

Method 300 may proceed with inserting the interlocking protrusion of thesecond structure into the interlocking opening of the first structureduring operation 312. When operation 310 is present, operation 312 maybe performed immediately after operation 310 while the interlockingprotrusion is still at its low temperature and, therefore, is shrunk.Performing operation 312 at this stage allows the interlockingprotrusion to be inserted into the interlocking opening. In someembodiments, operations 310 and 312 may overlap such that cooling iscontinued while the interlocking protrusion is inserted into theinterlocking opening. If another shape memory alloy structure (e.g., theoptional third structure) needs to be interlocked with the firststructure, then the interlocking protrusion of this other structure maybe inserted into an additional interlocking opening of the firststructure during operation 312 as well. In this case, two or more shapememory alloy structures may be interlocked (e.g., by heating) with thefirst structure at the same time. Alternatively, each shape memory alloystructure may be interlocked with the first structure using a separatesubset of operations 312 and 314. For example, a second structure may beinterlocked with the first structure prior to inserting the interlockingprotrusion of the optional third structure into an additionalinterlocking opening of the first structure.

Operation 312 is illustrated in FIGS. 4A and 4B. Specifically, FIG. 4Ais a schematic cross-sectional view of first structure 102 and secondstructure 104 prior to inserting interlocking protrusion 210 intointerlocking opening 200. First structure 102 and second structure 104are already aligned with respect to each other. In this example, theinsertion direction corresponds to the Z axis. Prior to and duringinsertion operation 312, the distance between outer protrusion corners212 a and 212 b (shown as L1 in FIG. 4A) is less than the distancebetween outer opening corners 202 a and 202 b (shown as L2 in FIG. 4A,with L2>L1). As such, outer opening corners 202 a and 202 b do not blockouter protrusion corners 212 a and 212 b during insertion ofinterlocking protrusion 210 into interlocking opening 200. It should benoted that the distance between inner opening corners 204 a and 204 b(shown as L3 in FIG. 4A) is even greater than the distance between outeropening corners 202 a and 202 b (i.e., L3>L2). While the shape ofinterlocking opening 200 remains constant during all interlockingoperations (as such, distances L2 and L3 also remain constant), theshape of interlocking protrusion 210 changes during installation. Thischange of the shape also changes distance L1 as further described below.

FIG. 4B is a schematic cross-sectional view of first structure 102 andsecond structure 104 after insertion of interlocking protrusion 210 intointerlocking opening 200 but prior to heating interlocking protrusion210, in accordance with some embodiments. The shape of interlockingprotrusion 210 is the same as in FIG. 4A and, if needed, interlockingprotrusion 210 can still be removed from interlocking opening 200 atthis stage. Outer opening corners 202 a and 202 b may contact innerprotrusion corners 214 a and 214 b. However, inner opening corners 204 aand 204 b may be separated from outer protrusion corners 212 a and 212 bat this stage.

Returning to FIG. 3, method 300 may proceed with heating at least theinterlocking protrusion of the second structure during operation 314.Specifically, the interlocking protrusion of the second structure may beheated to its activation temperatures, which may be at least about 350°F. or even at least about 400° F. in some embodiments. As describedabove, the activation temperature depends on the composition of theshape memory alloy. In some embodiments, operation 314 may involve alocalized heating of the interlocking protrusion of the second structuresuch that other portion of the second structure remain unheated toheated below the activation temperature.

During heating operation 314, the interlocking protrusion of the secondstructure changes its shape and engages the interlocking opening of thesecond structure. FIG. 4C is a schematic cross-sectional view of firststructure 102 and second structure 104 after these two structures areinterlocked. Similar to FIG. 4B, interlocking protrusion 210 is insertedinto interlocking opening 200. However, interlocking protrusion 210shown in FIG. 4C has a different shape than the interlocking protrusionshown in FIG. 4B. Specifically, the distance between outer protrusioncorners 212 a and 212 b has increased during heating of interlockingprotrusion 210. As such, interlocking protrusion 210 shown in FIG. 4Ccannot move relative interlocking opening 200 at least in one direction,which may be referred to as an engagement direction. This distance maybe greater than the distance between outer opening corners 202 a and 202b and these corners will retain interlocking protrusion 210 ininterlocking opening 200. As shown in FIG. 4C, outer protrusion corners212 a and 212 b may engage inner opening corners 204 a and 204 b

In some embodiments, method 300 also involves disengaging the secondstructure from the first structure during operation 316 formaintainability. This disengagement is generally not performed in anoperating environment.

Examples of Aircraft Application

Examples of the disclosure may be described in the context of anaircraft manufacturing and service method 1100 as shown in FIG. 5 andaircraft 1102 as shown in FIG. 6. During pre-production, illustrativemethod 1100 may include specification and design 1104 of the aircraft1102 and material procurement 1106. During production, component andsubassembly manufacturing 1108 and system integration 1110 of aircraft1102 take place. Thereafter, aircraft 1102 may go through certificationand delivery 1112 to be placed in service 1114. While in service by acustomer, aircraft 1102 is scheduled for routine maintenance and service1116 (which may also include modification, reconfiguration,refurbishment, and so on). Assemblies including composite structuresinterlocked with shape memory alloys may be used at these variousstages, such as material procurement 1106 and component and subassemblymanufacturing 1108.

Each of the processes of illustrative method 1100 may be performed orcarried out by a system integrator, a third party, and/or an operator(e.g., a customer). For the purposes of this description, a systemintegrator may include, without limitation, any number of aircraftmanufacturers and major-system subcontractors; a third party mayinclude, without limitation, any number of vendors, subcontractors, andsuppliers; and an operator may be an airline, leasing company, militaryentity, service organization, and so on.

As shown in FIG. 6, aircraft 1102 produced by illustrative method 1100may include airframe 1118 with a plurality of high-level systems 1120and interior 1122.

Examples of high-level systems 1120 include one or more of propulsionsystem 1124, electrical system 1126, hydraulic system 1128, andenvironmental system 1130. Any number of other systems may be included.Although an aerospace example is shown, the principles disclosed hereinmay be applied to other industries, such as the automotive industry.Accordingly, in addition to aircraft 1102, the principles disclosedherein may apply to other vehicles, e.g., land vehicles, marinevehicles, space vehicles, etc.

Apparatus and methods shown or described herein may be employed duringany one or more of the stages of the aircraft manufacturing and servicemethod 1100. For example, components or subassemblies corresponding tocomponent and subassembly manufacturing 1108 may be fabricated ormanufactured in a manner similar to components or subassemblies producedwhile aircraft 1102 is in service. Also, one or more aspects of theapparatus, method, or combination thereof may be utilized duringoperations 1108 and 1110, for example, by substantially expeditingassembly of or reducing the cost of aircraft 1102. Similarly, one ormore aspects of the apparatus or method realizations, or a combinationthereof, may be utilized, for example and without limitation, whileaircraft 1102 is in service, e.g., maintenance and service 1116.

CONCLUSION

Different examples and aspects of the apparatus and methods aredisclosed herein that include a variety of components, features, andfunctionality. It should be understood that the various examples andaspects of the apparatus and methods disclosed herein may include any ofthe components, features, and functionality of any of the other examplesand aspects of the apparatus and methods disclosed herein in anycombination, and all of such possibilities are intended to be within thespirit and scope of the present disclosure.

Many modifications and other examples of the disclosure set forth hereinwill come to mind to one skilled in the art to which the disclosurepertains having the benefit of the teachings presented in the foregoingdescriptions and the associated drawings.

What is claimed is:
 1. A method of forming an assembly comprising afirst structure, a second structure, and a third structure, the methodcomprising: inserting an interlocking protrusion of the second structureinto a first interlocking opening of the first structure, the firststructure comprising a composite material, the second structure formedfrom a shape memory alloy and comprising an interlocking step and aflange, disposed on opposite ends of the second structure; inserting aninterlocking protrusion of the third structure into a secondinterlocking opening of the first structure, the third structure formedfrom the shape memory alloy, wherein the third structure comprises aninterlocking step and a flange, disposed on opposite ends of the thirdstructure, wherein the interlocking step of the third structure lockswith the interlocking step of the second structure and protrudes into athird interlocking opening of the first structure, wherein the thirdstructure is separate from the second structure and form, together withthe second structure, a sleeve around the first structure, and whereinthe flange of the third structure contacts the flange of the secondstructure and together extend away from the first structure; heating atleast the interlocking protrusion of the second structure, wherein,during the heating, the interlocking protrusion of the second structurechanges shape and locks within the first interlocking opening of thefirst structure; and heating at least the interlocking protrusion of thethird structure, wherein, during the heating, the interlockingprotrusion of the third structure changes shape and locks within thesecond interlocking opening of the first structure.
 2. The method ofclaim 1, further comprising training the second structure, whereintraining the second structure comprises heating the interlockingprotrusion of the second structure and, while heated, changing the shapeof the interlocking protrusion of the second structure.
 3. The method ofclaim 2, wherein training the second structure comprises cooling theinterlocking protrusion of the second structure and, while cooled,changing the shape of the interlocking protrusion of the secondstructure.
 4. The method of claim 1, wherein the interlocking protrusionof the second structure comprises a first outer protrusion corner and asecond outer protrusion corner, wherein the interlocking opening of thefirst structure comprises a first outer opening corner and a secondouter opening corner, wherein, prior to heating, a distance between thefirst outer protrusion corner and the second outer protrusion corner ofthe interlocking protrusion of the second structure is less than adistance between the first outer opening corner and the second outeropening corner of the interlocking opening of the first structure, andwherein, after heating, the distance between the first outer protrusioncorner and the second outer protrusion corner of the interlockingprotrusion of the second structure is greater than the distance betweenthe first outer opening corner and the second outer opening corner ofthe interlocking opening of the first structure.
 5. The method of claim1, further comprising consolidating the composite material of the firststructure prior to inserting the interlocking protrusion of the secondstructure into the interlocking opening of the first structure.
 6. Themethod of claim 5, further comprising, after consolidating the compositematerial of the first structure, forming the interlocking opening in thefirst structure.
 7. The method of claim 1, wherein the interlockingprotrusion of the third structure is inserted into the secondinterlocking opening of the first structure prior to heating at leastthe interlocking protrusion of the second structure.
 8. The method ofclaim 1, wherein the interlocking protrusion of the third structure isinserted into the second interlocking opening of the first structureafter heating at least the interlocking protrusion of the secondstructure.
 9. The method of claim 1, further comprising, prior toheating at least the interlocking protrusion of the second structure,cooling at least the interlocking protrusion of the second structure.10. The method of claim 1, further comprising disengaging the secondstructure from the first structure.
 11. The method of claim 2, whereinthe shape memory alloy is a one-way shape memory alloy such that theinterlocking protrusion of the second structure retains the shape whenthe shape memory alloy is cooled.
 12. The method of claim 1, wherein thecomposite material is braided.
 13. The method of claim 1, wherein theshape memory alloy is selected from the group consisting ofnickel-titanium based alloys, indium-titanium based alloys,nickel-aluminum based alloys, copper-zinc alloys, copper-aluminumalloys, copper-gold alloys, copper-tin alloys, gold-cadmium basedalloys, iron-platinum based alloys, iron-palladium based alloys,silver-cadmium based alloys, indium-cadmium based alloys andmanganese-copper based alloys.
 14. The method of claim 1, wherein across-section of a portion of the first structure is one of asubstantially round shape, a substantially square shape, or asubstantially rectangular shape.
 15. The method of claim 3, wherein,after the cooling, the sleeve formed by the second structure and thethird structure has a post-recovery interference with the firststructure of between about 0.5% and 3%.
 16. The method of claim 3,wherein, after the cooling, the sleeve formed by the second structureand the third structure has a shrink-fit configuration around the firststructure.
 17. The method of claim 1, wherein the second structurecomprises a flange protrusion, positioned at an interface of the flangewith a remaining portion of the second structure, and wherein the flangeprotrusion protrudes into a fourth interlocking opening of the firststructure.
 18. The method of claim 17, wherein the first interlockingopening, the second interlocking opening, the third interlockingopening, and the fourth interlocking opening of the first structure areevenly distributed around a perimeter of the first structure.
 19. Themethod of claim 1, wherein the flange of the second structure comprisesopening, for inserting a fastener.
 20. The method of claim 19, whereinthe flange of the third structure comprises an opening, for insertingthe fastener and co-centered with the opening in the flange of thesecond structure.
 21. The method of claim 1, further comprisingdisengaging the second structure from the first structure anddisengaging third structure from the first structure.
 22. The method ofclaim 1, wherein the interlocking step of the third structure locks withthe interlocking step of the second structure in a removable manner.